Several types of electronic identification systems are known. Optical systems typically provide electronic means for optically reading features presented in a defined pattern (typically holes in a punched card) which comprises an identifier code recognizable by the system. Optical systems suffer several disadvantages including the fact that they are frequently easily circumvented since the optical identifier code is often easily duplicated. Furthermore, optical systems may suffer a degradation in performance due to wearing of the optically-encoded identifier and due to the presence of dirt or other foreign matter on either the optical reader, the identifier, or both.
Magnetically encoded electronic identification systems usually offer better security than optically encoded systems since the magnetic code on an identifier is invisible (typically, the identifier comprises a substrate having a strip of magnetic material which is magnetized in a predetermined pattern which defines the identifier code). However, magnetic systems suffer several disadvantages including susceptibility to wear (for example, a magnetic oxide strip placed upon a card-type identifier substrate may eventually wear off); the magnetic code on the identifier may be accidentally altered or erased; and, dirt or other foreign matter on the magnetic reader, the identifier, or both, may degrade system performance by introducing errors when the system attempts to read the code on the identifier.
An object of the present invention is to provide an electronic identification system which offers security comparable to or better than that attainable by other systems while circumventing the disadvantages discussed above. A particular object is to provide an electronic identification system having a reader which may be used outdoors. A related object is to provide such a system which does not impose severe constraints upon parameters such as the required distance between the identifier and the reader, if the identifier code is to be read successfully. For example, a magnetically encoded identifier must typically be positioned no more than about 0.003 inches from the magnetic reader if the magnetic identifier code is to be read successfully. An object of the present invention is to provide an electronic identification system which may operate if the gap between the reader and the identifier is about 0.05 inches. A further related object is to provide such a system which will operate if a substantial portion of the gap between the reader and the identifier includes accumulated dirt or other foreign matter.